The present invention relates to an electrical power generation system of the type having an electrical generator for generating DC and wherein a variable parameter relating to the generated DC is sensed in a feedforward approach in order to control the output of an inverter which inverts the DC into controlled AC.
Copending U.S. patent application Ser. No. 07/911,549 filed on Jul. 9, 1992 disclosed an inverter control system which senses both a variable parameter relating to the DC input supplied to an inverter and the output of the inverter in order to control that output. That system is particularly useful in electrical power generation systems such as those employing permanent magnet generators driven by variable speed devices for supplying variable frequency electrical power to a variable speed, constant frequency (VSCF) system. As the variable speed device varies its speed, the frequency of the output from the generator varies. In a VSCF system, the variable frequency output from the generator is rectified to produce DC. If the frequency of the input to the rectifier varies, the voltage level of the DC output of the rectifier will vary. The DC voltage supplied by the rectifier in such an electrical power generation system can vary by 2:1 or more. Because a normal inverter system for inverting such DC into AC output has time delays associated with the inverter, with the inverter controller and with any filters used in the inverter system, the control of the output AC by a VSCF system in response to changes in the input DC is delayed.
Copending patent application, having Ser. No. 454,434 filed on Dec. 20, 1989 and assigned to the same assignee as the present application, discloses an inverter system for providing a stepped output utilizing plural inverters. The system shown therein responds to the AC output for controlling the phase between the inverter outputs in order to control the AC output. A stepped inverter is also shown in U.S. Pat. No. 3,775,662. Such a stepped-waveform inverter generates an output having a stepped shape that generally approximates a sine wave. The purpose of approximating a sine wave is to reduce the size of the filters provided at the output of the inverter that are used to remove unwanted harmonics. Such systems use feedback to control the inverter output, but often there is a generator control loop as well in order to regulate the input DC supplied to the inverter.
Systems of the type shown in copending U.S. Pat. application Ser. No. 454,434 filed on Dec. 20, 1989 can be used with the present invention, although the present invention can be used with other inverters as well. If the DC supplied to the inverter can be sensed and used as a control input, the response time for controlling the AC supplied by the inverter can be made much faster and control of the output AC does not have to be delayed as a result of the time delays inherent in such systems. Moreover, sensing the input DC in a feedforward approach also permits omission of the generator loop.